1. Field of Invention
The present invention is directed to a method and apparatus measuring transmission delay.
2. Description of Related Art
Presently, Internet Protocol (IP) services are being used to transmit data in real time. Such data may include audio data, video data, time critical service data and other forms of real time data. For example, two parties may wish to transmit two-way speech over the Internet. Because data transmitted over the Internet may be subject to delays and losses, these delays and losses may result in unintelligible speech transmissions. Designers of software and hardware that are utilized for speech transmission must take into consideration such delays and losses. Unfortunately, tools used to model delays may not provide accurate results.
Existing programs may be used to calculate the approximate Internet round-trip delay. To attempt to approximate a one-way delay, the user such a program must manually divide the round trip delay in half. This may lead to inaccurate and variable results because a return path of an Internet connection may be very different from the forward path.
Systems, such as Global Positioning Systems (GPS), may also be used to approximate Internet delay. The GPS may be used to synchronize two computers, send a data packet in one direction and measure the time it takes to send and receive the data packet. Unfortunately, the use of GPS to approximate Internet delay is expensive, complicated and inconvenient.
The invention provides an apparatus and method of measuring delay over a packetized network from a first terminal to a second terminal. A one-way delay is not approximated by an average of a two-way delay calculation, as in prior art. Also, less variation is introduced in the measurement of the delay by the use of a circuit switch network which utilizes fixed timeslots. In accordance with the invention, a first time difference is determined based on a round-trip delay over a combination of a packetized network and a circuit switched network. A second time difference is determined based on a round trip delay over the circuit switched network. Then a delay value is calculated by subtracting half of the second time difference from the first time difference.
The method may further include the sending of a first data transmission from the first terminal to the second terminal over the packetized network. The first data transmission is returned from the second terminal to the first terminal over a circuit switched network. A first time difference is determined between sending and receiving the first data transmission at the first terminal. A second data transmission is sent from the first terminal to the second terminal over the circuit switched network. A second time difference is determined between sending and receiving the second data transmission at the first terminal. A delay value is then calculated by subtracting half of the second time difference from the first time difference.
The packetized network may include an Internet system and the circuit switched network may include a Plain Old Telephone Service (POTS) network. The first data transmission may include a voice over Internet protocol data transmission and the second data transmission may include a voice over Internet protocol data transmission. The step of determining the first time difference may include setting a first time of transmission, determining a first time of reception, and calculating a difference between the first time of transmission and the first time of reception. The step of determining a second time difference may include setting a second time of transmission, determining a second time of reception, and calculating the difference between the second time of transmission and the second time of reception. The first data and second data transmission may include a generated tone. The data transmitted over the packetized network may include any form of signal and the data transmitted over the circuit switched network may include any form of signal or may include a generated tone.